The long-term objective of this proposal is to explore the pathological role of LPA, a component of oxidized LDL, in atherosclerosis. The driving hypothesis of the proposal is that one of the mechanisms by which LPA, a component of oxLDL, contributes to atherosclerosis is via up-regulation of TF expression. This hypothesis is based on our novel findings that 1) lipid lysophosphatidic acid (LPA), which has recently been shown to accumulate in high concentrations in atherosclerotic lesions and identified as a component of oxLDL, markedly increases TF mRNA, TF protein production and TF activity in SMC; 2) LPA induced-TF gene expression requires the activation of a particular G-protein, MAPK, PKC, the novel protein kinase D (PKD), and ribosome S6 kinase (p90RSK); and 3) LPA induces TF mRNA expression in heart, kidney and aorta of the living animal. This hypothesis is also supported by the observations recently reported by others: 1) Tissue factor (TF) plays an important role in the development of atherosclerosis; 2) LPA accumulates in high concentrations in atherosclerotic lesions; and 3) LPA induces neointimal formation in rat aorta. This hypothesis is innovative because in the development of atherosclerosis, the role of this phospholipid LPA, which forms during oxidation of LDL and is secreted from activated platelets, is totally unknown. The goals of this proposal will be achieved through the following specific aims: Aim 1:To identify and determine the role of LPA receptor, specific G-protein, and the particular isoform of protein kinase C in LPA-stimulated TF expression, using specific antagonists of LPA receptors, affinity labeling, antisense oligonucleotides, as well as the dominant-negative approach. Aim 2: To explore the novel biological role of PKD and p90RSK in TF gene regulation, using selective inhibitors and the dominant-negative strategy. Aim 3: Using a well-established atherosclerotic model-ApoE knockout mouse, to determine i) the role of LPA in the development of atherosclerosis; ii) the role of TF in mediating the pathological effect of LPA in atherosclerotic lesion development in vivo. The information obtained from the proposed studies may lead to the identification of novel therapeutic targets for the prevention and treatment of atherosclerosis. The proposed studies would also contribute to the understanding of the cellular signaling pathway that mediates the biological effects of LPA, specifically the effects on gene regulation in general. The proposed studies would also provide novel insight into the biological and cellular function of PKD and p90RSK in the vascular wall.